C. Gale

Isotype responses of infected, virus-vaccinated and peptide-vaccinated cattle to foot-and-mouth disease virus

An ELISA to measure bovine serum immunoglobulin isotypes (IgG1, IgG2, IgM and IgA) specific for foot-and-mouth disease virus (FMDV) or for synthetic FMDV peptides is described. Sera from cattle infected by FMDV, vaccinated with conventional inactivated virus vaccines or vaccinated with synthetic peptides were examined using this assay. Generally IgG subclasses dominated the antibody responses of all groups after an early IgM response had waned. An exception to this pattern was seen in the case of a group of immature calves given multiple or high doses of synthetic peptide and in which levels of IgM continued to rise until the end of the experimental period. Both infected animals and those vaccinated with inactivated virus mounted antibody responses in which IgG1 titres tended to predominate over those of IgG2. In some infected animals, an early IgG2 response was evident but resolution of lesions and clinical recovery did not occur until IgG1 antibody appeared in the serum some days later. In synthetic-peptide immunized animals the response was more variable but IgG1:IgG2 ratios at 21 days postvaccination were significantly lower than those of virus-vaccinated animals. It is proposed that differences in the isotype profiles induced by conventional FMD vaccines and those resulting from vaccination of cattle with synthetic FMDV peptides may in part account for the lower protective index of peptide-induced antibodies.

Modified-live infectious bovine rhinotracheitis virus vaccine expressing monomer and dimer forms of foot-and-mouth disease capsid protein epitopes on surface of hybrid virus particles

SummaryModified-live, attenuated infectious bovine rhinotracheitis (IBR) hybrid virus vaccines have been constructed by inserting in the major IBRV glycoprotein g III gene chemically synthesized deoxyribonucleotide sequences encoding the bovine growth hormone signal sequence and monomeric or dimeric forms of the foot and mouth disease virus (FMDV) VP 1 epitope sequences. The foreign DNA sequences were inserted at the N-terminal end of the IBRV g III coding sequence and were driven by the IBRV g III promoter. The sequences encoding the first 38 and the first 21 amino acids of the IBRV g III were deleted from the hybrid viruses containing inserts of the monomeric and dimeric FMDV epitope sequences, respectively, to avoid redundant signal sequences. Plaque immunoassay experiments with guinea pig and bovine anti-FMDV peptide antisera, and with anti-IBRV g III monoclonal antibodies demonstrated that IBRV-FMDV fusion proteins were expressed in virus-infected MDBK cells. Immunoelectron microscopy analyses demonstrated that the IBRV-FMDV fusion proteins were expressed as repeated structures on the surface of virus particles. Experiments showed that the recombinant IBRV-FMDV viruses protected cattle from IBRV (Cooper) challenge and induced anti-FMDV peptide antibodies, thereby demonstrating that the FMDV epitopes were expressed in vivo.

Mouse protection test as a predictor of the protective capacity of synthetic foot-and-mouth disease vaccines

A passive immunity test (MPT) in suckling mice for the quantification of protective anti-foot-and-mouth disease virus (FMDV) antibodies in serum is described. Comparisons with titres obtained using conventional serum neutralization tests show that for cattle given synthetic peptide vaccines this in vivo assay is a better indicator of protection, while for convalescent animals and virus-vaccinates both tests are equally valid predictors of immune status. Cleavage of Fc fragments from anti-virus or anti-peptide IgG results in a marked decrease in MPT titres although binding to virus in ELISA is unaffected, indicating that intact antibodies are required for in vivo clearance of FMDV. Cross-protection studies demonstrate that anti-peptide sera, while less potent than anti-viral sera in conferring passive immunity against FMDV challenge, have a wider protective range than anti-viral sera within the O serotype and also between O and A serotypes. Possible qualitative differences between anti-viral and anti-peptide sera are discussed in the light of these findings.

Maturation of functional antibody affinity in animals immunised with synthetic foot-and-mouth disease virus

A good correlation exists between specific neutralising antibody titre and protection against challenge with foot-and-mouth disease virus (FMDV) in infected or virus-vaccinated cattle, but not in the case of animals immunised with synthetic FMDV peptides. Therefore, mechanisms other than simple neutralisation are likely to be important in vivo. Antibody affinity may influence the protective capacity of sera from immunised animals and experiments were carried out to measure the functional affinity for synthetic FMDV peptide of sera from guinea pigs and cattle given various synthetic vaccines. In guinea pigs given a single dose of synthetic vaccine, antibody affinity increased with time after immunisation. In cattle, however, administration of a second dose of peptide 21 days after the first markedly retarded the process of affinity maturation. For guinea pig sera of equivalent neutralising activity, those of higher functional affinity had higher protective indices than those of lower functional affinity. Knowledge of the importance of antibody affinity in protection against FMD is important for an improved understanding of the mechanisms of protection and for the design of novel vaccines.

Modified-Live Infectious Bovine Rhinotracheitis Virus (IBRV) Vaccine Expressing Foot-and-Mouth Disease Virus (FMDV) Capsid Protein Epitopes on Surface of Hybrid Virus Particles

Foot-and-Mouth Disease (FMD) is a highly contagious disease of cattle and other cloven hoofed animals caused by a Picornavirus. It is enzootic in most South American countries, where hundreds of outbreaks are recorded each year, and endemic in many Asian, Middle East, African and European countries. The disease can spread rapidly due to its short incubation period and contagious nature and has a dramatic impact on livestock production and trade. In countries where FMD is endemic, binary ethylenimine-inactivated vaccines have been widely used to control disease. Annual production of FMD vaccine worldwide is probably between 700 and 800 million doses. Nearly 500 million doses are applied to cattle annually (Bahnemann, 1990). Yet, despite intensive vaccination programs, outbreaks of FMD occurred in 22 countries in the last quarter of 1989 (Foreign Animal Disease Report of USDA-APHIS,No. 18-2. Summer 1990).

Protection Induced by Synthetic Peptides Corresponding to Three Serotypes in Foot and Mouth Disease Virus

Foot and Mouth Disease (FMD) is a highly contagious disease which primarily affects cloven-hoofed animals. It is a disease of major economic importance. Mortality from FMD is low, except in young animals where it can be quite high. The disease is debilitating, spreads rapidly and requires only a short incubation period for establishing visible disease symptoms in infected animals. An outbreak of the disease can be economically devastating. In countries where the disease is endemic, the commonly used method of control is vaccination with an inactivated virus preparation. FMD vaccines, while proven to be effective, are not without risk. Outbreaks of the disease have been linked to vaccines which were improperly inactivated. Infections have also been traced to the escape of virus from production facilities. For these reasons, the developments in synthetic approaches to vaccination have attracted the attention of scientists working towards the control of this disease (Bittle et al.,1982; Pfaff et al., 1985; DiMarchi, et al., 1986).